1. Field of the Invention
This invention relates to a coating composition which provides under irradiation with ultraviolet rays, a crosslinked and cured coating film excellent in abrasion resistance, surface smoothness, flexibility, heat resistance, solvent resistance, durability and adhesion to the substrate. It also relates to a process for preparing synthetic resin shaped articles by using this coating composition, which shaped articles are excellent in abrasion resistance and adhesion and are made of polydiethylene glycol bisallylcarbonate (which may also be called "polyallyl diglycol carbonate" and is hereinafter referred to as "PDAC" for brevity).
2. Description of the Prior Art
Synthetic resin shaped articles prepared from polymethyl methacrylate resins, polystyrene resins, polycarbonate resins, PDAC resins, unsaturated polyester resins, epoxy resins and other similar resins have a light weight and are excellent in their impact resistance, and these synthetic resins are cheap and can easily be molded. Because of these various advantages, these synthetic resin shaped articles have been used in various fields and new uses of these synthetic resin shaped articles have been developed in various fields. However, these synthetic resin shaped articles are poor in abrasion resistance, and therefore, the surfaces are readily damaged by contact, abrasion or scratching with a hard article. Damage caused on the surfaces of these shaped articles lower the commercial value thereof drastically and shorten the service lives of these shaped articles. Therefore, it has eagerly been desired to improve the abrasion resistance of the surface in these synthetic resin shaped articles.
Among the synthetic resin shaped articles, PDAC resin shaped articles are advantageous in that, since PDAC resin shaped articles are prepared by cell casting, they have reduced residual molding strains and optical strains as compared with other thermoplastic resin shaped articles which are prepared by injection molding and the like. Furthermore, since PDAC resin shaped articles are cross-linkable and curable, they exhibit a relatively high surface hardness as compared with other thermoplastic resin shaped articles. Therefore, PDAC resin shaped articles have widely been used in recent years as spectacle lenses and optical lens parts. However, the abrasion resistance and surface hardness of the PDAC resin shaped articles are not completely satisfactory and, therefore, enhancement of these characteristics is eagerly desired.
Various methods have heretofore been proposed as means for eliminating the defects of various synthetic resin shaped articles. For example, there can be mentioned a method in which a coating material, comprised of a resin composition comprising a silicone or melamine type resin, is coated on the surface of a synthetic resin shaped article and then, the coating material is heated to be thereby condensed to yield a crosslinked coating film having an improved abrasion resistance on the synthetic resin shaped article, and a method in which a polyfunctional monomer, containing at least two polymerizable groups in the molecule, is coated on the surface of a synthetic resin shaped article and, then, the coated shaped article is irradiated with active energy rays to form a crosslinked and cured coating film on the surface of the synthetic resin shaped article, whereby a synthetic resin shaped article having an excellent abrasion resistance is obtained. We have already made many proposals as described in Japanese Laid-open Patent Application Nos. 102936/1978, No. 104638/1978, No. 97663/1979 and No. 97633/1979.
Although the abrasion resistance of synthetic resin shaped articles is improved by the above-mentioned methods, these methods are still not completely satisfactory. Namely, in the method wherein a coating material, such as a silicone or melamine type resin, is coated on the shaped articles and then heated to be thereby crosslinked and cured, it is necessary to heat the coating material at a high temperature over a long period of time. In the method wherein a coating material, such as a polyfunctional monomer containing at least two polymerizable groups, is coated on the shaped article and then irradiated with active energy rays to be thereby crosslinked and cured, the irradiation with active energy rays must be conducted in an atmosphere of an expensive inert gas. Furthermore, both the methods have the disadvantage that the crosslinked, cured coating film exhibits a poor adhesion, particularly to crosslinkable and curable synthetic resins, such as PDAC.